I was introduced to resonant frequencies at about 10 years old with model aero engines. The important thing to bear in mind is whether the resonance is of sufficient magnitude to actually cause a problem. RF is affected by many things, not least the distribution of mass of the crank both longitudinally and radially, therefore the RF of an engine with a steel crank will be different than with a stock crank, likewise a lightened flywheel will affect RF.
As I remember the origimal question was about an otherwise stock bottom end, no mention was made of after market or ‘VHPD’ flywheels. The affects of RF are greatly reduced if the rotating assembly is effectively balanced.
Not all K series engines are rev limited at 7200, the VVC for example has a higher rev limit as do all Caterham SS engines, smack bang in the middle of the RF zone but I have not heard of a litany of broken cranks on stock VVC or SS engines.
Only recently you told us that an engine that was properly balanced was under less stress at 9000RPM than any of the engines I have built would be at idle, so should I now expect a number of broken cranks at idle?
I do not believe that the effects of RF are of sufficient magnitude to cause a breakage such as the one illustrated. That looks to me like a typical breakage due to unsympathetic dumping of the clutch.
BTW plenty of my engines are in Elises and Exiges…
Sorry Simon, but simply advertising the book everytime your doom mongering is challenged doesn’t wash.
What it boils down to is, once again, that you intimate that it is impossible to build an engine with any sort of level of reliability without help/parts/annointing by yourself.
I dont buy it.
Mainly because there are thousands of engines out there happily revving through the RF zone who’s owners dont have to collect the bits of their cranks in a bin liner.
It is right and proper that something that causes a problem to an engine should be investigated, but a modicum of perspective is required to sort out the catastrophic from the merely annoying. I do not need to ‘learn’ about RF.
If it were as large a problem as you intimate then the statistics would show it to be, in my direct experience, they do not.
The K series has a torsional damper (absorber would be a better description) which attenuates the torsional oscillations which might otherwise worsen the affects of RF.
Removal of the the ‘damper’ and replacement with a lightweight single mass pulley can exacerbate the affects of RF, I would not recommend removal.
However sensible reduction of the overall mass of the rotational parts of the engine and the moment of inertia can raise the RPM at which the RF occurs, a properly lightened and balanced flywheel can move this significantly up the RPM range and out of the way of any sensible RPM.
Reduction of torsional vibrations by retaining or improving the absorber can also reduce the feedback into the system and further reduce the affects of RF.
In truth there is hardly a competition crank out there that sports “ideal” counterweights - many are 30%, perhaps Chris can enlighten us on this years Cosworth F1 practice?
I could tell you, but then unfortunately I’d have to kill you.
Lets also be clear the K series does not have a damper, it has an absorber which absorbs torsional forces and then puts them back in the system, a damper would absorb the energy and dissipate it as heat.
A torsional absorber will work at any RPM, it may be less effective at certain speeds but it is still worth having as my post affirms.
Resonant frequency moves in a constant relationship between elasiticity and mass just as a tuning fork would, lighten a tuning fork and its frequency goes up, make it of lower tensile material with greater elasticity and its frequency reponse gets lower. Effective lowering of the mass by decreasing flywheel weight is a good way of moving the natural FR of the crankset beyond the RPM where it is a problem.
Nobody except you has mentoned the VHPD flywheel, the original post was about a stock bottom end.
You have to be a bit blinkered to say that a broken crank is merely annoying, what I said was that you need to have some perspective and analyse what is truly problematical and can be shown to be so, or what happens to be the latest bit of reading material and this week 9 minute wonder.
I welcome research from accredited sources, so far I haven’t seen any from your direction.
Caterham do a variety of different flywheels of varying lightness and effectivity. Why would I want to design my own when the work has already been done.
Here is a quote from a well known source regarding dampers and absorbers…
"Often, the vibration attenuating devices on the free end of an engine crankshaft are incorrectly referred to as “DAMPERS”. In most cases, they are ABSORBERS. (That’s not semantics. A damper dissipates energy, typically as heat. An absorber alternately stores and releases energy to counteract vibration).
The elastomeric (“metal-ring-on-rubber-spring”) devices used by the automotive industry are ABSORBERS which are tuned to counteract vibration at the frequency where the particular engine generates its worst torsional excitation."
Is that clear enough?
Whether those cranks are a problem in this particular situation depends on the exact circumstances, RPM used, rotating mass, mod of usage, flywheel weight, secondary out of balance forces etc.etc that these brakages occurred under. I doubt wheter any of them were on otherwise stock engines as put forward by the original posting. It wouldnt surprise me if many of the steel cranks were run with no absorber and at crank speeds well in excess of the 8000RPM suggested.
Some really interesting info here. Cheers all round. It really does add to the knowledge base of technophobes like myself. Sadly the more I learn about engines, the less I realise I know.
The book is a long way off…I want to do at least two SC Ks before I commit to print and try and beat the 450bhp mark, but whenever it appears I have no doubt you will save yourself the time of looking at it , so any attempt to advertise it is entirely wasted on you.
simon
The book is still a long way, how many more years must we wait now then ?
By the way, you really must tone down you claims for the supercharged K, I think you started off at 400 which gave us all a good laugh and then you upped it to 450. But now I see you are hoping to beat 450 !! Maybe you are just saying that to wind everybody up, but if you really believe it then I suggest you have good look at your calculations again.
The book is a long way off…I want to do at least two SC Ks before I commit to print and try and beat the 450bhp mark, but whenever it appears I have no doubt you will save yourself the time of looking at it , so any attempt to advertise it is entirely wasted on you.
simon
The book is > still > a long way, how many more years must we wait now then ?
By the way, you really must tone down you claims for the supercharged K, I think you started off at 400 which gave us all a good laugh and then you upped it to 450. But now I see you are hoping to beat 450 !! Maybe you are just saying that to wind everybody up, but if you really believe it then I suggest you have good look at your calculations again.
BTW is Adrian Newey’s car running yet ?
Bernard
Bernard
Why don’t you just wait?
And does it really matter how long it takes me to build every engine, analyse all the issues, design all the parts, build the engines and prove them, or are you so desperate to have one yourself, after all Uldis’s engine met the one claim you all had so much to said I would never make - thay was easy to make 220bhp ages ago. Trust me I am doing it, I will not cut corners , and every last little detail of all the work will be in the book - some of it might even be useful for those that persist with old iron block designs?..who knows??
simon
So it’s still not going then ?
220 BHP is a only tad more than the K I built and put in my Elise over 4 1/2 years ago, haven’t you moved on since then ?
Nice to know that the whole world is wrong and you are right…
You mention that the K series ‘damper’ is tuned to the specific frequency of the engine, whose resonant frquency is determined by the mass and elasticity of the rotating masses.
Pardon my scepticism, but the Rover ‘damper’ is common across all engine sizes 1100, 1400, 1600 and 1800. The cranks on the shorter stroke engines are both lighter and stiffer (more bearing overlap) and have lighter flywheels, their resonant frequency will be very different from the 1800 and yet they use the same ‘damper’… ho-hum. So much for the damper being ‘tuned’ to the specifics for that particular engine.
Bernard, wasnt Peter Carmichaels 1800 engine doing 250BHP+ 5 or 6 years ago now?
thay was easy to make 220bhp ages ago…
Easy… that’s a good one, how many RR visits, exhausts, airboxes to just scrape in, didn’t yours just have one RR visit Bernard and on softer cams?
Yes, several, but that was because I wanted to come up with a different exhaust.
Could have just bought a good one, but:
a) it wasn’t split in the middle,
b) it wasn’t as light as what I have now,
c) wasn’t easy to repack.
Unfortunately I have the only exhaust that meets this criteria, as Jim didn’t want to proceed down this path. Too few S1’s and the owners are too grumpy
On the trumpet length I could have just bought Bernard’s setup but then I also wanted something different, with an eye n keeping the boot.
Haven’t succeeded yet (in keeping the boot) but I’m almost there.
BTW, the engine has been left untouched, not even the cam timing changed, more like to see what effect does every change have.